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  • Hi, this is Kate from MinuteEarth with, uh, hands.

  • Anyway, when I want to write, flip a pancake, or take adorable hyena pictures, like most people, I use my right hand.

  • Because despite being a near-mirror image of my right, my left hand is *terrible* at this stuff.

  • Lots of other animals also have a so-called "preferred" side.

  • Gorillas generally use their right hand for tasks requiring dexterity, while orangutans use their left.

  • Many parrots hold seeds with their left foot.

  • And Brazilian spitting spiders tend to favor their left fore-legs while hunting.

  • And sure, it's weird that some animals prefer their left and some their right, but what's even weirder is why we have a preferred side at all.

  • Perhaps a hand-ier way to think about it is if having one "good" side is good, why don't we have two?

  • It likely comes down to efficiency.

  • Most animals have brains with two largely-independent sides that perform somewhat different functions and control different - and, weirdly - opposite sides of our bodies.

  • Like, when I write my name, neurons in the left side of my brain send electrical signals to neurons in my right hand to tell it what to do.

  • But building and operating that neural circuit takes a lot of time and a lot of energy - and training that limb to write decently takes even more.

  • To write decently with my left hand, because of the quirky two-sidedness of our brains, I'd need an entirely different circuit, which would take a ton more time and energy to build, operate, and train.

  • Instead, it's much more efficient to rely on a single circuit for writing.

  • What's more, the more I use that circuit, the more I reinforce the neural connections from the brain to my right hand, making that hand even... well... handier, and the more likely I am to use it for other jobs.

  • Voilà - handedness.

  • This efficiency explanation is still somewhat theoretical, but evidence from all sorts of animals shows that having a preferred side can provide an advantage.

  • When scientists gave a food-finding test to parrots, some of whom had a strong side preference and some didn't - the strongly-sided birds did twice as well.

  • What's more, when the task got harder and the birds had to use a series of coordinated motions to get a snack hanging from a string, the strongly-sided birds were way better at figuring out a clever solution.

  • And look, during this more complicated task, the "un-preferred" side had something important to do too, just like how my left hand holds and steadies the paper when I'm writing, or the camera when I'm snapping a picture.

  • These jobs are often - literally - supporting roles, but they, too, require circuitry to perform, and training to perform well.

  • So, maybe our so-called "weaker" side isn't actually weak after all; it's just optimized for different jobs.

  • Without it, we wouldn't be able to hammer in a nail, play the guitar, catch and throw a baseball, perform heart surgery, or deftly wield a sword and shield.

  • Of course, there's that question of why I - along with most humans - would swing a sword with my right hand, while far fewer would choose their left.

  • But that's a question for another video, as this one is already out of hand.

  • The human body is really strange - we could go on and on about it.

  • And we actually have: We made MinuteBody, an entire series of videos about the weird workings of, well, us.

  • You can check out the first season exclusively on Nebula, a platform built by independent education-y creators like us as a place to experiment and try out new ideas.

  • And now CuriosityStream - a documentary streaming service that loves supporting creators - has teamed up with Nebula to launch the second season of MinuteBody.

  • The newest episode comes out today!

  • As part of our partnership, when you sign up for CuriosityStream at, you'll also get Nebula for free.

  • So, for just fifteen bucks a year, you'll not only get access to CuriosityStream's huge library of high-quality content like "What Animals See," you'll also get free access to tons of creative stuff on Nebula from the folks behind Real Engineering, Wendover, Tom Scott - and all new episodes of MinuteBody.

  • Come check it out!

Hi, this is Kate from MinuteEarth with, uh, hands.

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